The present invention relates to a novel single-part photographic bleach-fixing precursor composition that can be used to form a photographic bleach-fixing composition that, in turn, can be used for photoprocessing of photographic silver halide materials. In particular, this invention relates to a single-part bleach-fixing precursor composition comprising predominantly ferrous-ligand complexes. This invention also relates to various methods of using the precursor composition.
The basic process for obtaining color images from exposed color photographic silver halide materials includes several steps of photochemical processing using appropriate photochemical compositions.
Photographic color developing compositions are used to process color photographic materials such as color photographic films and papers to provide the desired dye images early in the photoprocessing method. Such compositions generally contain color developing agents, for example 4-amino-3-methyl-N-(2-methane sulfonamidoethyl)aniline, as reducing agents to react with suitable color forming couplers to form the desired dyes. U.S. Pat. No. 4,892,804 (Vincent et al.) describes conventional color developing compositions that have found considerable commercial success in the photographic industry.
To obtain useful color images, it is usually necessary to remove all of the silver from the photographic element after color development. This is sometimes known as xe2x80x9cdesilveringxe2x80x9d. Removal of silver is generally accomplished by oxidizing the metallic silver in what is known as a xe2x80x9cbleachingxe2x80x9d step using a bleaching agent, and then dissolving the oxidized silver and undeveloped silver halide with a silver xe2x80x9csolventxe2x80x9d or fixing agent in what is known as a xe2x80x9cfixingxe2x80x9d step.
It has become common for the processing of certain photographic elements, notably color photographic papers, to combine the bleaching and fixing operations into a single xe2x80x9cbleach-fixingxe2x80x9d operation that can be carried out in one or more processing steps. Bleach-fixing is usually carried out using a composition that includes both a photographic bleaching agent and a photographic fixing agent, as described for example in U.S. Pat. No. 4,033,771 (Borton et al.).
The most common bleaching agents for color photographic processing are complexes of ferric [Fe(III)] ion and various organic chelating ligands (such as aminopolycarboxylic acids), of which there are hundreds of possibilities, all with varying photographic bleaching abilities and biodegradability. Common organic chelating ligands used as part of bleaching agents for photographic color film processing include ethylenediaminetetraacetic acid (EDTA), 1,3-propylenediaminetetraacetic acid (PDTA) and nitrilotriacetic acid (NTA).
Also known are bleaching, bleach-fixing compositions, and processing methods that utilize a ferric complex of one or more of several alkyliminodiacetic acids (such as methyliminodiacetic acid or MIDA) that are known to be more biodegradable than other common organic chelating ligands such as EDTA. Other photographic bleaching agents using similar organic chelating ligands are described in U.S. Pat. No. 5,061,608 (Foster et al.) in which the ferric bleaching agent is advantageously combined with specific aliphatic carboxylic acids to reduce dye stains.
Typical photographic fixing agents include thiosulfates, sulfites, thiocyanates, and mixtures thereof that readily solubilize or xe2x80x9cdissolvexe2x80x9d silver ion in the processed photographic materials, as described for example in U.S. Pat. No. 5,633,124 (Schmittou et al.).
As pointed out in U.S. Pat. No. 5,055,382 (Long et al.), when photographic materials are processed in bleach-fixing steps, the bleach-fixing composition is generally formulated from two or more xe2x80x9cpartsxe2x80x9d, each xe2x80x9cpartxe2x80x9d or solution typically containing one or more (but not all) of the photochemicals necessary for the processing reactions. For example, one xe2x80x9cpartxe2x80x9d usually contains the conventional ferric bleaching agent, and another xe2x80x9cpartxe2x80x9d usually contains a thiosulfate fixing agent(s) and a sulfite preservative. These xe2x80x9cpartsxe2x80x9d are sometimes provided together in a photochemical processing xe2x80x9ckitxe2x80x9d. If all of the chemicals are formulated in a single solution, storage stability is reduced or nonexistent since unwanted chemical interactions among components are inevitable. For example, ferric bleaching agents, sulfite preservatives, and thiosulfate fixing agents are inherently reactive, thereby degrading solution effectiveness and storage stability.
It is also often desired in photographic processing to xe2x80x9cregeneratexe2x80x9d a xe2x80x9cseasonedxe2x80x9d bleaching or bleach-fixing composition that has been used extensively by adding depleted photochemicals to reconstitute the desired replenisher solution. One way of regenerating such compositions is to mix what is known as a xe2x80x9cregeneratorxe2x80x9d with a portion of the xe2x80x9cseasonedxe2x80x9d composition to form a replenisher solution that can be added back to the processing vessel. A variety of photographic ferric bleach regenerator compositions are known, for example, for processing color reversal materials as described for example in U.S. Pat. No. 5,652,087 (Craver et al.) and U.S. Pat. No. 5,834,170 (Craver et al.).
Throughout the photographic industry, there is a desire to provide xe2x80x9cconcentratedxe2x80x9d photoprocessing chemicals to reduce handling, transportation and storage costs. A number of successes have been achieved, for example by Eastman Kodak Company, to provide concentrated color developing compositions. The effort directed to providing concentrated bleach-fixing compositions, and especially in a single-part format, has encountered numerous hurdles.
In the form in which they are currently used, it has generally not been feasible to formulate, package, transport and store either working strength or concentrated bleach-fixing compositions in a single-part format. It is to this need in the photographic industry that the present invention is directed.
The problems described above have been overcome with a single-part photographic bleach-fixing precursor composition having a pH of from about 4 to about 10 and comprising:
at least 0.05 mol/l of one or more iron-ligand complexes,
at least 0.15 mol/l of one or more thiosulfates as the sole photographic fixing agents, and
optionally, one or more sulfites,
provided that at least 50 mol % of the iron present in the concentrated composition is in the form of Fe(II).
Further, this invention provides a method of providing a color photographic image comprising:
A) color developing an imagewise exposed color photographic silver halide material,
B) contacting the color developed color photographic silver halide material with a bleach-fixing solution for sufficient time to remove at least 95% of the silver in the color developed color photographic silver halide material, and
C) replenishing the bleach-fixing solution by adding to it a bleach-fixing replenisher solution prepared by mixing:
overflow from the bleach-fixing solution or water, and
the single-part photographic bleach-fixing precursor composition described above,
wherein the mixed volume ratio of the overflow or water to the single-part photographic bleach-fixing precursor composition is from about 50:1 to about 1:1.
This invention further provides a method of regenerating a spent bleach-fixing solution comprising mixing:
a seasoned bleach-fixing solution, and
the single-part, concentrated photographic bleach-fixing precursor composition described above,
wherein the mixed volume ratio of the seasoned bleach-fixing solution to the single-part photographic bleach-fixing precursor composition is from about 50:1 to about 1:1.
Still further, a method of providing a color image comprises contacting an imagewise exposed, color developed color photographic silver halide material with the single-part bleach-fixing precursor composition described above, diluted or undiluted, provided that prior to or during the contact, a sufficient amount of Fe (II) in the bleach-fixing precursor composition is oxidized to Fe (III) to bleach the imagewise exposed, color developed color photographic silver halide material.
In addition, the present invention provides a photographic processing kit comprising:
a) the single-part photographic bleach-fixing precursor composition described, and
b) either a composition comprising a Fe(III)-ligand complex, a composition comprising a ferrous ion oxidant, or both compositions.
Alternatively, the photographic processing kit comprises:
a) the single-part photographic bleach-fixing precursor composition described above, and
b) one or more additional photographic processing compositions.
For example, one useful photographic processing kit of this invention is a single-use processing kit that comprises at least the following multiple photographic photoprocessing liquid concentrates, each concentrate having a volume designed for dilution to the same predetermined volume of working strength photographic processing solution:
a) the single-part photographic bleach-fixing precursor composition described above,
b) single-part or two-part photographic color developing concentrate compositions,
c) a single-part photographic final rinsing or stabilizing concentrate composition, and optionally,
d) a single-part composition comprising a Fe(III)-ligand complex, a composition comprising a ferrous ion oxidant, or both compositions.
The present invention provides a considerable advance in the photoprocessing art by providing a composition that can be used to provide a bleach-fixing composition, that is stable for long-term storage, that is in a single-part format, and can be in concentrated form. Unwanted chemical interactions are critically minimized for these advantages to be achieved.
These desired benefits are obtained by using predominantly ferrous [Fe(II)] compounds in the precursor composition of this invention. By xe2x80x9cpredominantlyxe2x80x9d is meant that more than 50 mol % of all iron in the composition is in the form of Fe(II). Preferably, at least 65 mol % of all iron in the composition is in the form of Fe(II), and more preferably from about 70 to 100 mol % of all iron in the composition is in the form of Fe(II).
By xe2x80x9cprecursor compositionxe2x80x9d is meant that the composition of this invention is not generally a useful bleach-fixing composition itself, but upon oxidation of sufficient amounts of the Fe(II) ions to Fe(III) ions, the composition can then converted into a useful bleach-fixing composition. Thus, a bleach-fixing composition can be xe2x80x9cgeneratedxe2x80x9d from the precursor composition of this invention with appropriate oxidation of the ferrous ions. The precursor composition is stable since the Fe(II) compounds and other active photochemicals therein do not adversely interact. However, when the composition is to be used in the various methods described herein, Fe(II) ions can be oxidized to Fe(III) ions in any suitable and convenient manner.
The bleach-fixing precursor compositions of this invention can be provided in photoprocessing kits along with other useful processing compositions or oxidant compositions. In one embodiment, the photographic processing kit comprises compositions that are designed for xe2x80x9csingle-usexe2x80x9d, that is the kit solutions are designed for processing one or more photographic materials and then being discarded. All of the concentrate compositions in this kit have quality chemical formulations at volumes such that when each composition is diluted to the same predetermined volume, the results are ready-to-use working strength solutions. Thus, all of the chemical compositions are readily scaleable to useful volumes at the desired dilution rates.